1. Field of the Invention
The present invention relates to high transmission green dye for LCD, dye dispersion comprising the dye, coloring composition comprising the dye dispersion, color filter comprising the coloring composition, and synthetic method thereof.
2. Background of the Invention
A color filter used in Liquid Crystal Display (LCD) is used for materialize color images in the Display, which can be prepared through a process consisting of coating pigments on a basic circuit board with various methods, and curing and patterning them. The color filter is one that each of 3 color pixel parts is formed on a transparent circuit board as like a glass. The color filter used in a display device or a solid state image sensor usually has a coloring pattern of the three primary colors comprising Red®, green (G) and Blue (B) and play a role in coloring a light passing through or segregating it to the 3 primary colors. Dyes displaying red, green, and blue consist of fine particles, namely pigments, and these pigments display each of red, green, and blue color by mixing dyes representing similar colors rather than being used independently to obtain a color display property in a desired range.
Recently, technology development of LDC toward larger screen and higher definition has been advanced and its usage has been expanded sharply from a display for laptop computer to a monitor for a desktop computer and television monitor. In these situations, the color filter used in LCD is required to have high color purity. Especially in high definition display making high definition image display possible, it becomes important to satisfy this requirement. A light passing through a color filter is to be colored with the color of each pixel and colors of the lights are synthesized to form a color image. Therefore, a color filter having very high purity pixel is required as certain 3 colors of RGB making it possible.
Besides due to propagation of digital camera and camera equipped mobile phone, demand of solid state image sensors such as CCD image sensor has increased remarkably also. As the color filter is used as a key device of these displays or optical elements, demand on cost reduction as well as demand on high definition of the color filter increases.
Dyes used in the color filter are required to have following properties: Having a desirable light absorption property in color reproduction; having no development of optical faults such as light scattering or color non-uniformity of solid state image sensor causing contrast lowering of LCD or optical density non-uniformity causing coarse sensation; having proper resisting properties such as thermal resistance, light resistance, and damp heat resistance; and being capable of preparation of thin film.
Demands on LCD with high definition, namely improved contrast and color purity increase and it is required for improvement of contrast that the particle size of dyes (organic pigments) in photosensitive resin composition for formation of color filter is further smaller. In addition, it is important also to increase content of dyes (such as organic pigments) against solids of the photosensitive resin composition for improvement of color purity.
Besides, in the recent color filter for solid state image sensors such as CCD, high definition is required further. Therefore, miniaturization of dye is desired to inhibit color non-uniformity by coarse particles of the dye.
Currently, a metal halide phthalocyanine dye or a metal halide phthalocyanine pigment is used generally for forming green pixel. In concrete, dyes or pigments with metal halide phthalocyanine structure where at least 8 halogen atoms per phthalocyanine molecule are combined with benzene ring are used as a green dye constituting the green pixels of color filter.
Although Pigment Green 36 has been used mainly among them, its transmission degree is relatively low, so development of dye for improving that has been progressed. As a result of the development, Pigment Green 58 comprising zinc polyhalide phthalocyanine was developed as a dye for overcoming the demerit of Pigment Green 38 and suggested to be used as a dye for color filter.
The dye or the pigment is required to contain following properties: Having a desirable absorption property in color reproduction; and having good fastness property in its application environment including light resistance, thermal resistance, and resistance to oxidative gas such as ozone. Additionally, when the dye is a pigment, it is substantially insoluble in water or organic solvent and it is necessary to contain following properties: having good fastness resisting chemical; and giving no damage to desirable absorption properties in molecular dispersion even in being used as particles. The requirements may be controlled with strength and weakness of intermolecular interaction and it is difficult to make both of them coexist because they are in trade off relationship.
Under these situations, a technology using a dye instead of a pigment has been suggested. When using a dye instead of a pigment, accomplishment of high resolution is expected by solving problems such as color non-uniformity and coarse sensation in the color filter for solid state image sensor and improvement of optical properties such as contrast or haze is expected in LCD or Organic Light-Emitting Display (OLED).
However, coloring curable composition containing dyes has following problems also:
(1) The dyes in molecular dispersion state have insufficient light resistance and thermal resistance generally compared with the pigments forming molecular aggregates; especially, when forming ITO (Indium tin oxide) film used widely as an electrode of LCD, there is a problem that optical properties are changed by high temperature process.
(2) The dyes in molecular dispersion state have insufficient solvent resistance generally compared with the pigments forming molecular aggregates;
(3) As the pigment tends to inhibit radical polymerization reaction, there are some difficulties in designing coloring curable composition in a system using the radical polymerization as a mean of curing;
(4) Conventional dyes have lower solubility in alkali aqueous solution or organic solvent, so it is difficult to obtain a coloring curable composition having a desired spectrum;
(5) The dyes are likely to interact with other ingredients in the coloring curable composition, so it is difficult to control solubility of exposure and non-exposure part (developing property);
(6) When molar extinction coefficient of the dye (ε) is low, it is needed to add large amount of the dye. Thus, it is required to reduce the amount of other ingredients such as polymeric chemical (monomer), binder, or photo-initiator in the coloring curable composition relatively; curing property, heat resistance after curing, and developing property of the composition are lowered.
Therefore, it is required to develop an improved dye used for preparing a color filter for LCD able to overcome the above mentioned disadvantages.